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Originally posted by blakep82
Heres the thing though, 4 itbs, 40mm, total venturi area, 20,105mm2
The ecotecs oringinal single throttle body, 61mm, area 11,309mm2 making 136bhp.
Do I really need bigger? Or am I missing some throttle body basics here?

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Originally posted by blakep82
So, converting to efi from bike carbs, which is mainly driven by finding parts which make the swap easy andcheap, rather than maximum power potential (just need this running first, can refine it later)

Hopefully Dale bailey performance will see this, but I'd like to open this to everyone too
I was originally going with 40mm zx9r carbs so got a manifold made to suit. Couldnt stop them leaking fuel due to the angle they had to sit at, so efi had to be the way forward.
So manifold is limited to 40mm just now, itbs ive found that fit, spaced well, and cheap are also 40mm

Looking at bailey performance facebook page, theres a duratec which had 40mm bodies, but dale says duratecs really need 45mm minimum. I see that as a future upgrade for me though, get it running first, upgrade power with bigger bodies and manifold when it starts getting too slow for me!

Heres the thing though, 4 itbs, 40mm, total venturi area, 20,105mm2
The ecotecs oringinal single throttle body, 61mm, area 11,309mm2 making 136bhp.
Do I really need bigger? Or am I missing some throttle body basics here?

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Originally posted by BaileyPerformance
Looking at your picture, I suggest you angle your throttle bodies at the same angle as the inlet port, you've got a nasty sharp bend in the manifold which will really hurt power.

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Originally posted by blakep82
thats good news on the tank to swirl pot line! means that can stay as it is

i know what you mean about the bend in the inlet. thats a throwback to the carbs, where it was the only way they would fit so i had to design it that way. the inside of the runners is smooth and rounded though, so no sharp corners inside. again, that kinda comes back to what i was saying before (and what you suggested in an email) concentrate on getting it working with minimum fuss for now, and future upgrades will include bigger throttle bodies (if required) and a new manifold made specifically for them.
if i went for maximum power now, where do i go when i get bored of it? right now i just need it done, IVA, and refine later

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Originally posted by BaileyPerformance
Hi Blake,

An engine with a single throttle body, like most cars, feeds all 4 cylinders. An engine with 4 individual throttle has one per cylinder - but remember only one (well, one and abit) cylinders are drawing air at a time. So, in fact the common plenum with a single large throttle appears to have the edge over 4 smaller throttles. You cant just add up the airflow capability of 4 throttles and compare to the single throttle, its more like one throttle of the set of 4 compared to the single throttle.

The performance increase normally seen with individual throttle bodes is more to do with the direct airflow path allowing the engine to breathe at higher RPM, the more direct path to the valve the better as the engine does not need to suck as hard, quicker cylinder filling means more complete fill at high RPM.

The duratec has a large inlet port as standard, so seems to respond better to larger throttle bodies. The good thing about fuel injection is its more forgiving that carbs if you go too big on throttle size, carbs rely on vacuum across the jet to get the fuel, injection does not.

We have always opted for 45mm Jenveys on any 2.0L engine, regardless of tune, but would opt for 40 DCOEs (if customer wanted carbs) if the engine was stock, 45s if tuned as over carbing a stock engine can affect drivablity.

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